Scientists locate and remove specific neuron that causes itching

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Have you ever wondered what causes you to itch? Sure, an outside stimulus coming into contact with your skin will do the trick, but why are you suddenly itchy when you’re pretty sure nothing touched that spot on your arm? The running theories were that itches are some kind of pain so mild that it felt like an itch, or that, essentially, some nerves were acting up for a minute. Now, however, a group of scientists have isolated a specific neuron that causes us to itch, and doesn’t seem to do much else.

Two Johns Hopkins neuroscientists, Liang Hong and Xinzhong Dong, found a protein receptor — dubbed MrgprA3 — on some neurons that have nerve endings in the skin. When observed, the team found that certain chemicals caused the neurons to send electrical signals, but painful stimuli — as opposed to the innocuous chemicals — did not cause the signals to fire. To test those findings, scientists removed all of the MrgprA3 neurons from a group of lab mice, and found that the mice didn’t respond to itchy stimuli, whereas they still responded to painful stimuli.

At the very least, the team found that the neurons that contain the MrgprA3 protein receptor cause itching. To identify whether or not the MrgprA3 receptors respond to other feelings, the scientists engineered a receptor that reacts to capsaicin — the substance that makes a pepper spicy. The team stuck the receptor into the MrgprA3 neurons of mice that didn’t have a capsaicin receptor. So, if the MrgprA3 neurons are responsible for itching, when capsaicin is injected into the mice, it should cause them to itch instead of feel the pain of being injected with capsaicin. The scientists injected the mice with capsaicin, and the mice scratched themselves rather than felt pain, thus proving that the MrgprA3 neurons are specific to feeling itchy.

The experiment shows that itching is separate from other sensations, and that should lead toward remedies for itching maladies, such as poison ivy, or perhaps chickenpox. Maybe we’ll one day have a pill to take to prevent itchiness when we come across a video on the internet featuring bugs.